Most sewage systems work on the gravity system. That is, sewage generated in a building, home, commercial structure or otherwise, flows by gravity from a sewage drain extending from a building to a sewage drain collection system, into sewage mains which ultimately connect to a sewage treatment plant. At the sewage treatment plant the sewage is treated so that environmentally acceptable effluents can be released. This basic concept, of course, requires the sewage treatment plant to be at a lower level than all of the buildings in which sewage is generated. While this can be accomplished in many instances, frequently there arises the need for a sewage treatment system which is located in such a way that total gravity drainage cannot be employed. For instance, if a home is constructed in an area wherein a hill or a valley lies between it and a gravity sewage draining system then some method must be provided for conveying the sewage under pressure to the point where it can be connected with a gravity drainage system.
To accomplish this purpose, pressure sewage systems are provided for collecting sewage drained from a home or other type of building, or toilet facilities, to a collection point where the sewage is pumped, under pressure, through a line that ultimately connects with a gravity sewage drainage system or to a sewage treatment facility. By providing a collection system including a grinder pump, the sewage may not only be moved under pressure but a grinder pump makes it possible to use substantially smaller diameter sewage transport pipes extending between the sewage collection site and the sewage gravity flow system than can normally be employed where gravity alone is relied upon for moving sewage. Thus, the use of sewage handling systems including grinder pumps are well-known.
One problem in the known sewer handling systems that employ a grinder pump is that of providing a control system for turning the pump on and off in response to the quantity of sewage that has collected. Control systems typically function based on the level of sewage in a collection vessel. The level can be detected by a float actuated switch, however, the environment in which such switches function has made the standard liquid level detector switches unreliable. Another problem with known types of liquid level switches is that they must operate in a harsh environment for a very extended length of time. Due to the environment, it is a highly disagreeable job to enter into the area where liquid level switches are located to do maintenance and repair. For this reason, it has long been an object in the use of sewage grinder pumps in sewage handling systems to provide liquid level detector systems that are highly dependable and substantially maintenance free. For background information relating to pressure sewage systems and to sewage grinder pump systems, reference may be had to the following previously issued United States Patents which are incorporated herein by reference.
______________________________________ U.S. Pat. No. INVENTOR TITLE ______________________________________ 3,667,692 Grace Pump Storage Grinder 3,857,517 Grace et al Anti-Siphon and Pump Priming For Sewage Grinder Pump 3,904,131 Farrell et al Pressure Sewer System 4,014,475 Grace et al Combined Manway and Collection Tank For Sewage Grinder 4,739,786 Parkinson Liquid Level Monitoring Assemblies 4,919,343 Van Luik et al Anti-Flooding Sewage Grinder Pump Liquid Level Control System In Separately Mounted Canister 5,044,566 Mitsch Sewage Pump With Self- Adjusting Cutters ______________________________________